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Abstract:

Methods and systems are provided for protecting a critical structure
during the administration of radiation treatment to a patient. A register
receives proposed positions for one or more radiation beams with respect
to a critical structure. A processor predicts a cumulative dose volume
for the critical structure based on the dose distribution, and determines
if the cumulative dose volume exceeds a tolerance value. If the
cumulative dose volume exceeds the tolerance value, the dose distribution
may be translated at least in part based on a relationship between the
cumulative dose volume and the dose distribution position.

Claims:

1. A method for protecting a critical structure during the administration
of radiation treatment to a patient, the method comprising the steps of:
(a) receiving, from a register, proposed positions for one or more
radiation beams with respect to a critical structure, wherein a
combination of the one or more radiation beams defines a dose
distribution having a dose distribution position; and at a processor, (b)
predicting a cumulative dose volume for the critical structure based on
the dose distribution, wherein the cumulative dose volume comprises a
volume of the critical structure that is predicted to receive more than a
specified radiation dose; (c) determining if the cumulative dose volume
exceeds a tolerance value; and (d) if the cumulative dose volume exceeds
the tolerance value, translating the dose distribution at least in part
based on a relationship between the cumulative dose volume and the dose
distribution position.

2. The method of claim 1, wherein the translating step comprises
determining a direction in which to translate the dose distribution with
respect to the critical structure, wherein the direction requires a
minimum amount of translation to achieve a cumulative dose volume equal
to the tolerance value.

3. The method of claim 2, wherein the translating step comprises
translating the dose distribution in the direction until the cumulative
dose volume is equal to the tolerance value.

4. The method of claim 1, wherein the translating step comprises
translating the dose distribution in a direction of a greatest rate of
decrease in cumulative dose volume.

5. The method of claim 1, wherein the translating step comprises
translating the dose distribution in a hybrid direction, wherein the
hybrid direction lies between (i) a direction requiring a minimum amount
of translation to achieve a cumulative dose volume equal to the tolerance
value, and (ii) a direction of a greatest decrease in cumulative dose
volume.

6. The method of claim 1, wherein the relationship is determined by
translating the dose distribution to proposed locations and calculating
the cumulative dose volume at each proposed location.

7. The method of claim 1, wherein, subsequent to translating the dose
distribution, the dose distribution intersects the critical structure.

8. The method of claim 1, comprising the step of generating an alert
indicating that the predicted radiation exposure exceeds the tolerance
value.

9. The method of claim 1, wherein the tolerance value is greater than
zero.

10. A system for protecting a critical structure during the
administration of radiation treatment to a patient, the system
comprising: (a) a register configured to store proposed positions for one
or more radiation beams with respect to at least one critical structure,
wherein a combination of the one or more radiation beams defines a dose
distribution having a dose distribution position; and (b) a processor
configured to: (i) predict a cumulative dose volume for the critical
structure based on the dose distribution, wherein the cumulative dose
volume comprises a volume of the critical structure that is predicted to
receive more than a specified radiation dose; (ii) determine if the
cumulative dose volume exceeds a tolerance value; and (iii) if the
cumulative dose volume exceeds the tolerance value, translate the dose
distribution at least in part based on a relationship between the
cumulative dose volume and the dose distribution position.

11. The system of claim 10, wherein the processor is configured to
determine a direction in which to translate the dose distribution with
respect to the critical structure, wherein the direction requires a
minimum amount of translation to achieve a cumulative dose volume equal
to the tolerance value.

12. The system of claim 11, wherein the processor is configured to
translate the dose distribution in the direction until the cumulative
dose volume is equal to the tolerance value.

13. The system of claim 10, wherein the processor is configured to
translate the dose distribution in a direction of a greatest rate of
decrease in cumulative dose volume.

14. The system of claim 10, wherein the processor is configured to
translate the dose distribution in a hybrid direction, wherein the hybrid
direction lies between (i) a direction requiring a minimum amount of
translation to achieve a cumulative dose volume equal to the tolerance
value, and (ii) a direction of a greatest decrease in cumulative dose
volume.

15. The system of claim 10, wherein, to determine the relationship, the
processor is configured to translate the dose distribution to proposed
locations and calculate the cumulative dose volume at each proposed
location.

16. The system of claim 10, wherein, subsequent to translation of the
dose distribution, the dose distribution intersects the critical
structure.

17. The system of claim 10, wherein the processor is further configured
to generate an alert indicating that the predicted radiation exposure
exceeds the tolerance value.

18. The system of claim 10, wherein the tolerance value is greater than
zero.

Description:

TECHNICAL FIELD

[0001] This invention relates to methods and systems for protecting
critical structures during the administration of radiation treatment to a
patient and, more particularly, to methods and systems for adjusting a
proposed dose distribution.

BACKGROUND INFORMATION

[0002] Tumors and lesions are pathological anatomies characterized by
abnormal growth of tissue resulting from a progressive, uncontrolled
multiplication of cells, while serving no physiological function.
Pathological anatomies can be treated with invasive procedures, such as
surgery, but these procedures can be risky and/or harmful for the
patient.

[0003] A non-invasive method to treat a pathological anatomy (e.g., tumor,
lesion, vascular malformation, nerve disorder, etc.) is external beam
radiation therapy. In one type of external beam radiation therapy, an
external radiation source is used to direct a sequence of x-ray beams at
a tumor site from multiple angles. As the angle of the radiation source
changes, each beam passes through the tumor site, but travels through a
different area of healthy tissue on its way to the tumor. Ideally, the
cumulative radiation dose at the tumor is high and the radiation dose to
healthy tissue is low.

[0004] Radiation therapy typically includes a planning phase in which
locations for the radiation beams are determined, and a treatment phase
in which the radiation beams are administered. During the planning phase,
a software package may be used to import three-dimensional (3-D) images,
such as computerized x-ray tomography (CT) scans, for delineating
structures to be targeted or avoided during treatment. A goal of the
planning phase is to identify a dose distribution (i.e., a collection of
radiation beams) that conforms to the tumor, while avoiding critical
structures or organs at risk, such as the spinal cord or healthy brain
tissue.

[0005] During the treatment phase and just prior to the administration of
radiation, 3-D images may again be collected to determine whether the
tumor has undergone morphological changes and/or moved with respect to
nearby critical structures. To account for any changes that have
occurred, the dose distribution identified during the planning phase may
need to be moved, adjusted, and/or completely reworked. For example, with
one approach, the proposed dose distribution is moved until it falls
outside of exclusion zones placed around the critical structures. With
another approach, the shape of the dose distribution is changed (e.g., by
adjusting the shapes and/or relative positions of the radiation beams)
until the dose distribution does not contact or intersect critical
structures. Unfortunately, adjusting the proposed dose distribution can
be a time consuming and expensive process.

[0006] Accordingly, a need exists for methods and systems that allow a
proposed dose distribution, identified during the planning phase, to be
utilized during the treatment phase with a minimal amount of adjustment,
despite morphological changes and/or movements that may have occurred
between a tumor and one or more critical structures.

SUMMARY OF THE INVENTION

[0007] The present invention provides methods and systems for protecting
anatomical structures during the administration of radiation treatment to
a patient. In certain embodiments, a proposed dose distribution is
identified during a planning phase and stored in a register. During a
treatment phase, a processor receives the dose distribution from the
register and predicts a radiation exposure (e.g., a cumulative dose
volume) for one or more critical structures. If the predicted radiation
exposure is too high, the dose distribution is translated until the
predicted radiation is below an acceptable threshold.

[0008] The methods and systems provided herein simplify the process of
utilizing a proposed dose distribution, identified during the planning
phase, for treatment during the treatment phase. Identifying a dose
distribution during the planning phase can be an expensive, time
consuming, and computationally intensive process. Further adjustments to
the dose distribution immediately prior to treatment involve additional
cost, time, and effort. The methods and systems provided herein
advantageously allow the proposed dose distribution to be utilized during
treatment with a minimal amount of adjustment.

[0009] In one aspect, a method is provided for protecting a critical
structure during the administration of radiation treatment to a patient.
The method includes the steps of (a) receiving, from a register, proposed
positions for one or more radiation beams with respect to a critical
structure, wherein a combination of the one or more radiation beams
defines a dose distribution having a dose distribution position, and, at
a processor, (b) predicting a cumulative dose volume for the critical
structure based on the dose distribution, wherein the cumulative dose
volume comprises a volume of the critical structure that is predicted to
receive more than a specified radiation dose, (c) determining if the
cumulative dose volume exceeds a tolerance value, and (d) if the
cumulative dose volume exceeds the tolerance value, translating the dose
distribution at least in part based on a relationship between the
cumulative dose volume and the dose distribution position.

[0010] In certain embodiments, the translating step includes determining a
direction in which to translate the dose distribution with respect to the
critical structure, wherein the direction requires a minimum amount of
translation to achieve a cumulative dose volume equal to the tolerance
value. The translating step may include translating the dose distribution
in the direction until the cumulative dose volume is equal to the
tolerance value. In one embodiment, the translating step includes
translating the dose distribution in a direction of a greatest rate of
decrease in cumulative dose volume. In another embodiment, the
translating step includes translating the dose distribution in a hybrid
direction, wherein the hybrid direction lies between (i) a direction
requiring a minimum amount of translation to achieve a cumulative dose
volume equal to the tolerance value, and (ii) a direction of a greatest
decrease in cumulative dose volume. The relationship between the
cumulative dose volume and the dose distribution position may be
determined by translating the dose distribution to proposed locations and
calculating the cumulative dose volume at each proposed location.
Subsequent to translating the dose distribution, the dose distribution
may intersect the critical structure. The method may also include the
step of generating an alert indicating that the predicted radiation
exposure exceeds the tolerance value, which may be greater than zero.

[0011] In another aspect, a system is provided for protecting a critical
structure during the administration of radiation treatment to a patient.
The system includes a register configured to store proposed positions for
one or more radiation beams with respect to at least one critical
structure, wherein a combination of the one or more radiation beams
defines a dose distribution having a dose distribution position. The
system also includes a processor configured to (i) predict a cumulative
dose volume for the critical structure based on the dose distribution,
wherein the cumulative dose volume comprises a volume of the critical
structure that is predicted to receive more than a specified radiation
dose, (ii)determine if the cumulative dose volume exceeds a tolerance
value, and (iii)if the cumulative dose volume exceeds the tolerance
value, translate the dose distribution at least in part based on a
relationship between the cumulative dose volume and the dose distribution
position.

[0012] In certain embodiments, the processor is configured to determine a
direction in which to translate the dose distribution with respect to the
critical structure, wherein the direction requires a minimum amount of
translation to achieve a cumulative dose volume equal to the tolerance
value. The processor may also be configured to translate the dose
distribution in the direction until the cumulative dose volume is equal
to the tolerance value. In one embodiment, the processor is configured to
translate the dose distribution in a direction of a greatest rate of
decrease in cumulative dose volume. In another embodiment, the processor
is configured to translate the dose distribution in a hybrid direction,
wherein the hybrid direction lies between (i) a direction requiring a
minimum amount of translation to achieve a cumulative dose volume equal
to the tolerance value, and (ii) a direction of a greatest decrease in
cumulative dose volume. To determine the relationship between the
cumulative dose volume and the dose distribution position, the processor
may be configured to translate the dose distribution to proposed
locations and calculate the cumulative dose volume at each proposed
location. Subsequent to translation of the dose distribution, the dose
distribution may intersect the critical structure. The processor may be
further configured to generate an alert indicating that the predicted
radiation exposure exceeds the tolerance value, which may be greater than
zero.

[0013] The foregoing and other objects, features and advantages of the
present invention disclosed herein, as well as the invention itself, will
be more fully understood from the following description of preferred
embodiments and claims, when read together with the accompanying
drawings. In the drawings, like reference characters generally refer to
the same parts throughout the different views. The drawings are not
necessarily to scale, emphasis instead generally being placed upon
illustrating the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In the drawings, like reference characters generally refer to the
same parts throughout the different views. Also, the drawings are not
necessarily to scale, emphasis instead generally being placed upon
illustrating the principles of the invention.

[0015] FIG. 1 is a schematic view of multiple radiation beams, a dose
distribution, and critical structures, in accordance with one embodiment
of the invention.

[0016] FIG. 2 is a schematic, cross-sectional view of a target, a dose
distribution, and a critical structure, during a planning phase, in
accordance with one embodiment of the invention.

[0017] FIGS. 3 and 4 are schematic, cross-sectional views of a target, a
dose distribution, and a critical structure, during a treatment phase, in
accordance with one embodiment of the invention.

[0018] FIG. 5 is a flowchart depicting a method for protecting a critical
structure during the administration of radiation treatment to a patient,
in accordance with one embodiment of the invention.

[0019] FIG. 6 is a graph of a cumulative dose volume histogram, in
accordance with one embodiment of the invention.

[0020] FIG. 7 is a flowchart depicting a portion of a method for
protecting a critical structure during the administration of radiation
treatment to a patient, in accordance with one embodiment of the
invention.

[0021] FIG. 8 is a schematic, cross-sectional view of a dose distribution
and a critical structure, in accordance with one embodiment of the
invention.

[0022] FIG. 9 is a schematic, cross-sectional view of a dose distribution
and a critical structure, in accordance with one embodiment of the
invention.

[0023] FIG. 10 is a two-dimensional plot of a relationship between
cumulative dose volume and a position of a dose distribution, in
accordance with an embodiment of the invention.

[0024] FIG. 11 is a flowchart depicting a portion of a method for
protecting a critical structure during the administration of radiation
treatment to a patient, in accordance with one embodiment of the
invention.

[0025] FIG. 12 is a flowchart depicting a portion of a method for
protecting a critical structure during the administration of radiation
treatment to a patient, in accordance with one embodiment of the
invention.

[0026] FIG. 13 is a schematic view of a critical structure having a more
sensitive portion and a less sensitive portion, in accordance with one
embodiment of the invention.

[0027] FIG. 14 is a schematic, perspective view of a device for
administering radiation to a patient, in accordance with one embodiment
of the invention.

DETAILED DESCRIPTION

[0028] Referring to FIG. 1, in certain embodiments, methods and systems
are provided for treating a target, such as a tumor or lesion, in a
patient with one or more beams 10 of radiation. As depicted, the one or
more beams 10 may project onto the target from different angles. The one
or more beams may avoid critical structures 12 and produce a
three-dimensional dose distribution 14, positioned over the target.
Positions and angles for the one or more beams 10 may be proposed during
a planning phase. A few days or weeks later, the proposed beams may be
administered to the patient during a treatment phase, following any
necessary adjustments.

[0029] In one embodiment, during the treatment planning phase, images are
obtained to identify the size, shape, and placement of the target and any
surrounding tissue or organs, including critical structures 12. The
images may be represented in two or three dimensions, and generated using
one or more techniques known in the art, such as three-dimensional
ultrasound imaging, CT scanning, magnetic resonance imaging, and/or PET
scanning Based on the shapes and positions of the target and any critical
structures, a proposed position and shape for the dose distribution may
be identified.

[0030] Determining the shapes and positions of the radiation beams 10 to
generate the proposed dose distribution 14 may be an expensive and
computationally intensive process. Beam shapes may be generated that
represent maximum projected shapes of the target for each planned beam
direction. Identifying beam shapes and directions may be repeated any
number of times, until the physician or other dosimetry specialist is
satisfied that the treatment plan is appropriate and that the prescribed
dose may be delivered to the target while sparing the health of
surrounding structures.

[0031] FIG. 2 is a schematic, cross-sectional view of a target 16, a dose
distribution 18, and a critical structure 20, obtained from an image of a
patient during the planning phase, in accordance with an embodiment of
the invention. The target 16 may be any anatomical feature such as a
cancerous organ, tumor, or lesion, such as a lymph node in the neck
region, a cancerous prostate, a tumor bed in a breast, or a lung tumor.
As depicted, the dose distribution 18 includes isocontours 21 of constant
radiation intensity. The radiation intensity may be greatest at an
isocenter 22 of the dose distribution 18 and lowest at an outer edge 24
of the dose distribution 18. In the depicted embodiment, a spacing D
between the target 16 and the critical structure 20 is sufficiently large
and allows the dose distribution 18 to be positioned over the target 16
without contacting the critical structure 20.

[0032] As described above, the target 16 and surrounding tissue and organs
can move and/or undergo morphological changes between the planning phase
and the treatment phase, and/or between treatment sessions (i.e.,
inter-fraction movements or changes). Some targets, such as lung tumors,
may move within a single treatment session (i.e., intra-fraction
movements). In some instances, the treatment sessions can occur over a
period of weeks or even months, giving rise to further uncertainties in
patient positioning and physiology. In addition, the planning phase may
occur substantially before the treatment phase or, in some cases,
immediately preceding the treatment phase. As the time span increases
between the phases, the target has a greater opportunity to grow, morph,
and/or change its positioning with respect to surrounding normal tissue
and healthy organs, thus resulting in a need for positional compensation
or dose distribution adjustment.

[0033] Due to breathing and other movements within the lungs, the location
of a lung tumor with respect to adjacent tissues can be especially
difficult to track and identify. Various measures have been developed to
mitigate this difficulty. For example, intra-fraction motion of lung
tumors may be mitigated by analyzing a patient's internal anatomy during
free-breathing. In addition, treatments may be based on estimated tumor
position, using gating, breath hold, or average tumor position over the
course of the breathing cycle. In the case of inter-fraction motion,
x-ray images of the patient may be taken prior to the start of a
treatment session. The images may then be analyzed for movement of the
tumor position, and the patient or patient support may be repositioned,
if necessary, to bring the tumor back into a desired position. Care must
be taken when repositioning the patient, however, as the positional
relationship between the tumor and nearby critical structures may also
change. It is important that the radiation dose to nearby critical
structures is not unnecessarily increased by corrective movements of the
patient in treatment setup.

[0034] Prior to a radiation treatment session, the technician obtains
updated images, such as three-dimensional ultrasound images, of the
target 16 and surrounding tissue that characterize the most current
position and shape of the target 16. The proposed dose distribution 18
may then be superimposed onto the target 16 to determine whether any
adjustments to the dose distribution 18 are required.

[0035] FIG. 3 is a schematic, cross-sectional view of the target 16, the
dose distribution 18, and the critical structure 20, obtained from an
image of the patient during the treatment phase. Comparing FIGS. 2 and 3,
it may be seen that the spacing D between the target 16 and the critical
structure 20 decreased during the time between the planning phase and the
treatment phase. As a result, when the proposed dose distribution 18 is
positioned over the target 16, the dose distribution 18 forms a region of
contact 26 with the critical structure 20. Administering the proposed
dose distribution 18 in this situation may expose the critical structure
to excessive radiation.

[0036] Referring to FIG. 4, in certain embodiments, methods and systems
are provided for adjusting the proposed dose distribution 18 from the
planning phase so that the target 16 receives an adequate dose and the
critical structure 20 receives a dose that is below an acceptable
threshold value. As depicted, in one embodiment, the methods and systems
achieve this result by translating the dose distribution 18 away from the
critical structure 20 until the dose to the critical structure 20 is
acceptable. Translating the dose distribution may include maintaining a
shape of the dose distribution 18 (e.g., by maintaining the shapes and
sizes of the radiation isocontours 21) and/or rotating the dose
distribution 18. As the dose distribution 18 is moved away from the
critical structure 20, the region of contact 26 between the dose
distribution 18 and the critical structure 20 may decrease.

[0037] In certain embodiments, the acceptable threshold value for the
critical structure 20 may be any value that results in an acceptable dose
to the critical structure 20. For example, the threshold value may be
less than about 2000 cGy, less than about 1000 cGy, less than about 500
cGy, less than about 200 cGy, less than about 100 cGy, or less than about
50 cGy. In one embodiment, the threshold value is greater than zero. For
example, when the dose distribution 18 has been translated to an
acceptable location, the dose distribution 18 may contact or intersect at
least a portion of the critical structure 20.

[0038] Referring to FIG. 5, in certain embodiments, a method 30 is
provided for protecting one or more critical structures during the
administration of radiation treatment to a patient. The method includes
the step of receiving (step 32), from a register 34, proposed positions
for one or more radiation beams with respect to at least one critical
structure. As described above, the one or more radiation beams define a
dose distribution. The method also includes predicting (step 36) a
radiation exposure for at least one critical structure based on the dose
distribution, and determining (step 38) if the predicted radiation
exposure exceeds a tolerance value. If the predicted radiation exposure
exceeds the tolerance value, the method 30 includes translating (step 40)
the dose distribution with respect to the at least one critical structure
until the predicted radiation exposure is below the tolerance value.
Steps 32, 36, 38, and 40 may be performed by a processor 42. The register
34 may be any known organized data storage facility (e.g., partitions in
RAM, etc.). In certain embodiments, the steps of method 30 are performed
by a system that includes the register 34 and the processor 42.

[0039] In certain embodiments, the predicted radiation exposure and the
tolerance value are defined in terms of a cumulative dose volume (CDV).
The CDV may be, for example, a percentage of a volume of tissue (e.g., a
critical structure) that receives or is predicted to receive a radiation
dose higher than a specified value. Referring to FIG. 6, the CDV may be
depicted in the form of a cumulative dose volume histogram, which shows
CDV as a function of radiation dose.

[0040] In one embodiment, the method 30 includes generating an alert
indicating that the predicted radiation exposure exceeds the tolerance
value. The alert may be, for example, visual (e.g., flashing lights or
indicators), audible (e.g., beeps or buzzes), and/or physical (e.g.,
vibration).

[0041] Referring to FIG. 7, the method 30 may also include determining a
direction in which to translate the dose distribution away from one or
more critical structures. For example, in certain embodiments, the
translating step 40 includes the steps of calculating (step 44) a
radiation gradient within the dose distribution, and moving (step 46) the
dose distribution in a direction of a maximum radiation gradient.

[0042] Referring to FIG. 8, the dose distribution 18 may include
irregularly shaped radiation isocontours 21 surrounding the isocenter 22.
Radiation gradients within the dose distribution 18 may be oriented in a
direction perpendicular to the isocontours 21. As described above, in one
embodiment, the methods and systems are used to identify a maximum
radiation gradient 48 within the dose distribution 18. The dose
distribution may then be translated in a direction of the maximum
radiation gradient 48. In one embodiment, the maximum radiation gradient
48 passes through the isocenter 22 of the dose distribution 18.

[0043] As depicted, in certain embodiments, the maximum radiation gradient
48 is located within the region of contact 26 between the dose
distribution 18 and the critical structure 20. For example, the processor
42 may be configured to identify the maximum radiation gradient 48 within
the region of contact 26 and to translate the dose distribution 18 in a
direction defined by the maximum radiation gradient 48. As depicted, the
direction of the maximum radiation gradient 48 may pass through or be
located at a point of intercept 50, which may be any point within the
region of contact 26 between the dose distribution 18 and the critical
structure 20. For example, the point of intercept 50 may be at a center
of the region of contact 26. In other embodiments, the point of intercept
50 is at a location of greatest overlap between the dose distribution 18
and the critical structure 20, and/or at a location of maximum radiation
exposure within the critical structure 20.

[0044] By moving the dose distribution 18 in the direction of the maximum
radiation gradient 48, the methods and systems described herein are
advantageously capable of reducing the radiation exposure (e.g., CDV) to
one or more critical structures in an efficient manner. For example, the
direction of the maximum radiation gradient 48 may be the direction in
which a given distance of translation of the dose distribution 18 will
produce the greatest reduction in radiation exposure to the critical
structure 20.

[0045] In certain embodiments, the radiation gradient (also referred to as
the radiation intensity gradient) at any point within a dose distribution
is a vector that points in the direction of the greatest rate of increase
in radiation intensity, and whose magnitude is the greatest rate of
change. For example, if the dose distribution has a radiation intensity
R, the radiation gradient at any x, y, z location within the dose
distribution may be determined from

∇ R ( x , y , z ) = ( ∂ R
∂ x , ∂ R ∂ y ,
∂ R ∂ z ) . ##EQU00001##

[0046] Partial derivatives of R with respect to x, y, and z may be
determined numerically using techniques (e.g., finite differences) that
are well known in the art.

[0047] Depending on the shapes and sizes of the critical structure and the
dose distribution, however, the direction of maximum radiation gradient
may not be the best or most efficient direction in which to translate the
dose distribution. For example, FIG. 9 depicts a two-dimensional
representation of a dose distribution 52 and a critical structure 54. A
maximum radiation gradient is indicated by a vector 56 in this figure.
The critical structure 54 is predicted to receive a high dose of
radiation in a region 58 defined by an isocontour 60. As depicted, given
the shapes and positions of the critical structure 54 and the dose
distribution 52, vector 56 may not define the best direction in which to
translate the dose distribution 52. Specifically, translating the dose
distribution 52 along vector 56 would not efficiently reduce the size of
the region 58. As a result, an excessive amount of translation may be
required to satisfy the tolerance value, which may cause the target to
receive less than a desired dose.

[0048] To identify a more efficient direction in which to translate the
dose distribution 50, in another embodiment, the dose distribution 50 is
translated according to a relationship between the CDV for the critical
structure 54 and the position of the dose distribution 50. Specifically,
the relationship may be used to identify a direction that requires the
least amount of translation before the CDV satisfies the tolerance value.
By following this approach, the direction of translation may take into
account both the radiation gradient within the dose distribution 50 and
the shapes and sizes of the critical structure 54 and the dose
distribution 52.

[0049] FIG. 10 is a two-dimensional plot showing a relationship between
CDV and the position of a dose distribution, in accordance with an
embodiment of the invention. The figure depicts CDV iso-percentages of
20%, 30%, 40%, 50%, 60%, and 70% as a function of displacement (i.e.,
Δx and Δy) of the dose distribution from its current position
(i.e., Δx=0 and Δy=0). Although the relationship is shown as
two-dimensional, this relationship may be, in reality, three-dimensional,
with iso-percentages defined by surfaces, rather than two-dimensional
curves. In the depicted embodiment, the CDV is 50% at zero displacement.
Stated differently, at the current position of the dose distribution, 50%
of the critical structure will receive a radiation dose greater than the
specified value, which may be, for example, 20 Gy.

[0050] In one embodiment, it may be desirable to reduce the CDV for the
critical structure from 50% to 30%. As depicted, a desired translation
direction for achieving the 30% CDV may be direction D1, which is a
direction in which the 30% iso-percentage curve may be reached with the
least amount of displacement. For comparison purposes, the direction
requiring the least amount of displacement to reach the 20%
iso-percentage curve is direction D2.

[0051] Referring to FIG. 11, in one embodiment, the translation step 40 of
the method 30, described above, includes calculating (step 62) a
relationship between the CDV and the position of the dose distribution.
The relationship may be calculated analytically and/or numerically. For
example, the dose distribution may be moved to various proposed locations
in the x, y, and z directions, and the CDV may be calculated at each
proposed location. Iso-percentages may be obtained by fitting curves or
surfaces through the calculated CDV values. As described above, the
method 30 may also include identifying (step 64) a translation direction
that requires the least amount of displacement of the dose distribution
before the CDV satisfies the tolerance value. Once the desired direction
for translating the dose distribution has been identified, the method 30
may also include translating (step 66) the dose distribution in the
desired direction until the CDV satisfies the tolerance value.

[0052] Referring to FIG. 12, in another embodiment, the CDV received by
the critical structure is reduced by displacing the dose distribution in
a direction of greatest rate of decrease in the CDV. Specifically, the
translating step 40 of method 30 may include calculating (step 68) a
direction of greatest rate of decrease in the CDV, and translating (step
70) the dose distribution in this direction. In the embodiment depicted
in FIG. 10, the direction of greatest rate of decrease in the CDV may be
direction D3. In one embodiment, the dose distribution is translated in
direction D3 to reduce the CDV as quickly as possible while maintaining a
desired dose for the target. This approach may be used, for example, when
large translations are not desirable and/or when there is no need to
reduce the CDV to a certain value. In one embodiment, the direction of
greatest decrease in the CDV is aligned with a gradient of the CDV.

[0053] In one embodiment, the systems and methods described herein provide
a sliding scale that allows an operator to choose how much emphasis to
put on maintaining a desired dose to the target, and how emphasis much to
put on sparing critical organs. For example, in the embodiment depicted
in FIG. 10, if an operator's goal is to reduce the CDV from 50% to 30%,
then the dose distribution may be moved along direction D1, which
corresponds to the closest point on the 30% iso-percentage line. On the
other hand, if the operator's goal is to reduce the CDV as quickly as
possible without trying to reach a particular CDV, then the dose
distribution may be translated along direction D3, which points in a
direction of greatest rate of decrease in CDV. In other embodiments, the
dose distribution is moved in a direction that lies between D1 and D3.
For example, depending on the value the operator selects on the sliding
scale, the system may move the dose distribution along direction D1,
direction D3, or in a direction that lies between those two directions.

[0054] In another embodiment, the systems and methods may move the dose
distribution a small (e.g., differential) amount in the direction of
greatest rate of decrease in CDV. Once the dose distribution has been
relocated, a new direction of greatest rate of decrease in CDV may be
calculated, and the dose distribution may be displaced again a small
amount in that new direction. This process of calculating the greatest
rate of decrease in CDV and translating the dose distribution in that
direction may be repeated a desired number of times. For example, the
process may be repeated until the CDV reaches the tolerance value. This
approach may be capable of identifying the least amount of translation
required to achieve a specified tolerance value.

[0055] In certain embodiments, the systems and methods described herein
attempt to satisfy more than one tolerance value. For example, the
patient situation may include multiple critical structures, each having
their own radiation exposure tolerance values. For example, one critical
structure may be a spinal cord having a low exposure tolerance, and
another critical structure may be a liver having a relatively high
exposure tolerance. The patient situation may also include a target
(e.g., a tumor) having a minimum dose tolerance. In one embodiment, a
goal of a treatment planning system is to produce a treatment plan that
satisfies these multiple tolerance values.

[0056] In another embodiment, the CDV of a critical structure is weighted
according to variations within the critical structure. For example, the
critical structure may have a portion that is more sensitive to
radiation, and another portion that is less sensitive to radiation. To
better protect the more sensitive portion, the CDV may be weighted such
that radiation exposure to the more sensitive portion disproportionately
increases the CDV. To illustrate this concept, FIG. 13 depicts a critical
structure 72 in which half of the critical structure is a more sensitive
portion 74, and the other half of the critical structure is a less
sensitive portion 76. In a hypothetical treatment plan, the CDV of the
more sensitive portion 74 may be 60%, and the CDV of the less sensitive
portion 76 may be 40%. Without weighing the CDVs of the two portions 74,
76 differently, the CDV for the critical structure 72 is 50% (i.e., the
average of 40% and 60%). If weights are applied, however, the CDV for the
more sensitive portion 74 is weighed more heavily than the CDV for the
less sensitive portion 76, and the CDV for the critical structure 72 is
greater than 50%. The higher CDV for the critical structure 72 protects
the more sensitive portion 72 by requiring a greater reduction in CDV to
satisfy the tolerance value. In one embodiment, the relationship between
CDV and the position of the dose distribution, as described above and
depicted in FIG. 10, is determined using a weighted CDV.

[0057] In certain embodiments, the methods and systems provided herein
translate the dose distribution in an iterative manner. For example, with
each iteration, the dose distribution may be translated by a translation
distance, and the radiation exposure to the critical structure may be
recalculated based on the new location of the dose distribution. If the
radiation exposure is still excessive (e.g., above an acceptable
threshold value), the dose distribution may be translated again by the
translation distance. In one embodiment, the translation distance may be
any distance that is capable of achieving a reduction of the radiation
exposure to the critical structure. The translation distance may be a
fixed value, or it may vary. For example, the translation distance may
change from one iteration to the next, and/or it may change from one
patient situation to the next, depending on the sizes and relative
positions of the target and any critical structures. In one embodiment,
the translation distance is a function of the radiation exposure to the
critical structure. For example, when the radiation exposure is large,
the translation distance may be large. When the radiation exposure is
small, the translation distance may be small. The translation distance
may be proportional to a difference between the radiation exposure and
the acceptable threshold value. Typical translation distances may be, for
example, about 5 cm, about 1 cm, about 0.5 cm, about 1 mm, or about 0.1
mm.

[0058] In certain embodiments, the methods and systems described herein
interface with a device that administers radiation to the patient. For
example, a dose distribution identified by the methods and systems may be
conveyed to the device, and the device may then expose the patient to
radiation according to the dose distribution.

[0059] The device used to administer the radiation may be any device
capable of delivering a beam of radiation for radiation treatment. The
device may include a single radiation source that is capable of moving
with respect to the patient to deliver one or more doses at different
positions and orientations. Alternatively, the device may include
multiple radiation sources that are capable of delivering multiple
radiation beams to the patient simultaneously.

[0060] Referring to FIG. 14, in one embodiment, a treatment device 80
includes a radiation source 82 that may be positioned around the patient
at various angles. The treatment device 80 may also include an imaging
system to obtain scans of the patient situation, including the sizes,
shapes, and positions of any tumors and critical structures. As depicted,
the imaging system may include an x-ray source 84 and an x-ray image
detector (imager) 86. In one embodiment, for example, the x-ray source 84
is configured to project x-ray beams through a patient positioned on a
treatment couch 88. The x-ray beams may be projected from various angular
positions (e.g., separated by 90 degrees) and aimed through the patient
toward the detector 86. Other numbers and configurations of imaging
sources and imagers are contemplated.

[0061] Treatment device 80 may be a gantry based (isocentric) intensity
modulated radiotherapy (IMRT) system. The radiation source 82 (e.g., a
LINAC) may be mounted on a gantry in such a way that it rotates in a
plane corresponding to an axial slice of the patient. Radiation may then
be delivered from several positions on the circular plane of rotation. In
IMRT, the shape of the radiation beam may be defined by a multi-leaf
collimator that allows portions of the beam to be blocked, so that the
remaining beam incident on the patient has a pre-defined shape. The
resulting system may generate arbitrarily shaped radiation beams that
intersect each other at an isocenter to deliver a dose distribution to
the target.

[0062] In certain embodiments, the device is a stereotactic frame system
such as the GAMMA KNIFE®, available from Elekta of Sweden. With such
a device, the systems and methods provided herein may determine the
selection and dose weighting assigned to a group of beams, in order to
best meet provided dose constraints.

[0063] In other embodiments, the device includes a radiation source
mounted on the end of a robotic arm having multiple (e.g., 5 or more)
degrees of freedom to position the radiation source at various angles
around the patient. The treatment device may include one or more x-ray
sources and one or more x-ray image detectors. In one embodiment, for
example, the one or more x-ray sources are configured to project x-ray
beams through the patient from two different angular positions.

[0064] In some embodiments, the register and processor may implement the
functionality of the present invention in hardware or software, or a
combination of both on a general-purpose computer. In addition, such a
program may set aside portions of a computer's random access memory to
provide control logic that affects one or more of the image manipulation,
fusion, alignment, and support device control. In such an embodiment, the
program may be written in any one of a number of high-level languages,
such as FORTRAN, PASCAL, C, C++, C#, Java, Tcl, or BASIC. Further, the
program can be written in a script, macro, or functionality embedded in
commercially available software, such as EXCEL or VISUAL BASIC.
Additionally, the software could be implemented in an assembly language
directed to a microprocessor resident on a computer. For example, the
software can be implemented in Intel 80×86 assembly language if it
is configured to run on an IBM PC or PC clone. The software may be
embedded on an article of manufacture including, but not limited to,
"computer-readable program means" such as a floppy disk, a hard disk, an
optical disk, a magnetic tape, a PROM, an EPROM, or CD-ROM.

[0065] While the invention has been particularly shown and described with
reference to specific embodiments, it should be understood by those
skilled in the area that various changes in form and detail may be made
therein without departing from the spirit and scope of the invention as
defined by the appended claims. The scope of the invention is thus
indicated by the appended claims and all changes which come within the
meaning and range of equivalency of the claims are therefore intended to
be embraced.

Patent applications by Jan-Jakob Sonke, Amsterdam NL

Patent applications by Marcel Van Herk, Amsterdam NL

Patent applications by Peter Remeijer, Amsterdam NL

Patent applications in class IRRADIATION OF OBJECTS OR MATERIAL

Patent applications in all subclasses IRRADIATION OF OBJECTS OR MATERIAL